The present invention relates to an illuminator for supplying a divergent illuminating beam from an area with predetermined energy distribution and dimensions.
The manufacture of integrated circuits involves the superimposing of levels in a semiconductor wafer (e.g. silicon or AsGa). For this purpose, windows are formed on the wafer making it possible to locate the implantation or processing by masking a photosensitive resin deposited on the wafer from a mask. At present, the most frequently used method is transfer by optical projection.
This projection can be carried out at scale 1, the mask being completely projected onto the wafer. It can also be carried out by splitting up the image, either by analysing the mask by a moving slot, or by using the photorepetition method with a reduction of scale.
In the latter case, during production it is necessary to optimise the production flow rate, more particularly by reducing the exposure time necessary for a good illumination. It is known to bring about a significant reduction in this time by using a laser source.
Due to its spatial and time coherence, the laser constitutes a special illuminating source. Its use in an optical image projection device leads to the appearance of a significant coherence noise. The nature of the illumination must therefore be modified in order to obtain an image with a good signal-to-noise ratio. For this purpose, it is possible to use a device which can average out the interference patterns produced by the coherence of the beam. It is also possible to use a rotary diffuser located in the path of the illuminating beam. The disadvantage of the diffuser is that it introduces a very large luminous energy loss, which partly cancels out the advantages resulting from the high available power of a laser.